I bought a Trident Aegis case and though it adds a bit of bulk and weight, feel it really will help protect my 520 should I drop it, which is what the case is designed to do. All the phones buttons/controls work perfectly and there are covers for the headphone jack and charging/data port to prevent crud from getting into them when not in use. Case comes with a screen protector but I already had a BodyGuardz protector on my screen so did not use the Trident one.
Got it off *Bay for $20 shipped.
Trident Aegis Case for Nokia Lumia 520 Blue | eBay